1. Field of the Invention
The present invention generally relates to video tape recorders and, more particularly, is directed to a so-called 8-mm video tape recorder.
2. Description of the Prior Art
According to the standards determined when the so-called 8-mm video tape recorder was originated, upon recording, a luminance signal is converted into an FM (frequency-modulated) luminance signal having a sync. (synchronizing) chip level of 4.2 MHz and a white peak level of 5.4 MHz as shown on the second row of FIG. 1. This FM luminance signal is recorded on a magnetic tape at every field period as a slant video track (this mode will hereinafter be referred to as "standard mode" and the above values are in accordance with the NTSC system).
When an audio signal is converted into a pulse-code modulated (PCM) audio signal and recorded on the magnetic tape, it is recorded according to the standards shown on the second row in FIG. 2. More specifically, the audio signal is quantized into a digital signal having a sampling frequency of 31.5 kHz (this sampling frequency is substantially twice the horizontal frequency) and one sample of 10 bits. After one sample of this digital signal is nonlinearly data-compressed in the form of 10 bits to 8 bits, this data-compressed digital signal is converted into a biphase mark signal. The biphase mark signal is recorded in the video track at its front over-scan interval over an angular extent of 36 degrees (this mode will hereinafter be referred to as "NRML mode").
In the 8-mm video tape recorder, a quality of image is improved in addition to the standards of the standard mode. That is, upon recording, the luminance signal is converted into an FM signal having a sync. chip level of 5.7 MHz and a white peak level of 7.7 MHz as shown on the third row of FIG. 1 and, this FM luminance signal is recorded on the magnetic tape at every field period as a slant video track (this mode will hereinafter be referred to as "High band mode").
It is proposed to improve the quality of sound of a PCM audio signal in accordance with the improvement of the quality of image. When the quality of sound is improved, it is proposed to employ a linear mode and a non-linear mode (they will hereinafter be referred to as "L mode" and "N mode").
That is, in the L mode, the audio signal is quantized into a digital signal in which a sampling frequency is any of 48 kHz, 44.1 kHz and 32 kHz and one sample is formed of 16 bits. This digital signal is converted in an eight-to-ten (8-10) conversion manner and, the converted digital signal is recorded in the video track at its front over-scan interval over an angular extent of 41 degrees.
In the N mode, as shown on the fourth row of FIG. 2, one sample of the quantized digital signal is non-linearly data-compressed in the form of 16 bits to 12 bits and then recorded similarly to the L mode.
Since the recorded signal involves an error correction code, an identification (ID) code or the like in actual practice, the Nyquist frequency (maximum recording frequency) and the minimum wavelength of the recorded signal on the magnetic tape are presented as shown in FIG. 3 (values on FIG. 3 are roughly estimated).
Therefore, according to the new standards of the PCM audio signal, the audio signal can be recorded and reproduced with characteristics equal to or higher than those of a CD (compact disc) and R-DAT (rotary-type digital audio tape recorder).
As described above, in the 8-mm video tape recorder, the standards of the standard mode and the NRML mode are determined and then the standard of the high band mode is added in accordance with the development of technology. Furthermore, the standards of L mode and the N mode are additionally provided.